When you are having this latency problem do you still have the same latency if you play on the GigaStudio keyboard? If there was no difference, that should rule out your sequencer/midi interface..
Though this shouldn\'t happen with the old drivers, you might want to install the new Mia drivers - I think new as of March of 2003.
Does it make a difference when you have the Mia mixer running?
When you are having this problem do a CTRL?ALT?DEL and look at what tasks are running then compare that to a list you have made when all is well.
Sorry no answers but maybe some actions to help narrow down the problem.